1. Field of the Invention
This invention relates to a radiation image read-out method and apparatus. This invention particularly relates to a radiation image read-out method and apparatus, wherein a radiation image having been stored on a stimulable phosphor sheet is read out with a line sensor.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a stimulable phosphor sheet, which comprises a substrate and a layer of the stimulable phosphor overlaid on the substrate. Stimulating rays, such as a laser beam, are deflected and caused to scan pixels in the radiation image, which has been stored on the stimulable phosphor sheet, one after another. The stimulating rays cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted successively from the pixels in the radiation image having been stored on the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal by photoelectric read-out means. The stimulable phosphor sheet, from which the image signal has been detected, is then exposed to erasing light, and radiation energy remaining thereon is thereby released.
Also, a novel radiation image recording and reproducing system aiming at enhancement of a detection quantum efficiency in the formation of the radiation image, i.e., a radiation absorptivity, a light emission efficiency, an emitted light pickup efficiency, and the like, has been proposed in, for example, Japanese Patent Application No. 11(1999)-372978. With the proposed radiation image recording and reproducing system, the radiation absorbing functions and the energy storing functions of the conventional stimulable phosphor are separated from each other, and a phosphor having good radiation absorbing characteristics and a phosphor having good light emission response characteristics are utilized respectively for radiation absorption and radiation image storage. The phosphor having good radiation absorbing characteristics (i.e., the phosphor for radiation absorption) is caused to absorb the radiation and to emit light having wavelengths falling within an ultraviolet to visible region. Also, the phosphor having good light emission response characteristics (i.e., the phosphor for energy storage) is caused to absorb the light, which has been emitted by the phosphor having good radiation absorbing characteristics, and to store energy of the emitted light. The phosphor having good light emission response characteristics, on which the energy of the emitted light has been stored, is then exposed to light having wavelengths falling within a visible to infrared region, which light causes the phosphor having good light emission response characteristics to emit light in accordance with the stored energy. The light having thus been emitted by the phosphor having good light emission response characteristics is successively detected with photoelectric read-out means, and an image signal is thereby obtained.
The image signal, which has been obtained from the radiation image recording and reproducing systems described above, is then subjected to image processing, such as gradation processing and processing in the frequency domain, such that a visible radiation image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness, can be obtained. The image signal having been obtained from the image processing is utilized for reproducing a visible image for diagnosis, or the like, on film or on a high resolution cathode ray tube (CRT) display device. In cases where the stimulable phosphor sheet, from which the image signal has been detected, is then exposed to the erasing light, and energy remaining on the stimulable phosphor sheet is thereby released, the erased stimulable phosphor sheet is capable of being used again for the recording of a radiation image.
Novel radiation image read-out apparatuses for use in the radiation image recording and reproducing systems described above have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540. In the proposed radiation image read-out apparatuses, from the point of view of keeping the emitted light detection time short, reducing the size of the apparatus, and keeping the cost low, a line light source for irradiating linear stimulating rays onto a stimulable phosphor sheet is utilized as a stimulating ray source, and a line sensor comprising a plurality of photoelectric conversion devices arrayed along the length direction of a linear area of the stimulable phosphor sheet, onto which linear area the stimulating rays are irradiated by the line light source, is utilized as photoelectric read-out means. (The length direction of the linear area of the stimulable phosphor sheet will hereinbelow be referred to as the main scanning direction.) Also, the proposed radiation image read-out apparatuses comprise scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet. (The direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet, will hereinbelow be referred to as the sub-scanning direction.)
However, the line sensor utilized in the radiation image recording and reproducing systems described above comprises the plurality of the photoelectric conversion devices arrayed along the main scanning direction, and the photoelectric conversion devices exhibit variation in sensitivity with respect to light emitted by the stimulable phosphor sheet. Therefore, the problems occur in that noise due to the variation in sensitivity with respect to light emitted by the stimulable phosphor sheet mixes in the output of the line sensor, and an image having good image quality cannot be obtained. For example, in cases where the line sensor is constituted of a charge coupled device (CCD) image sensor, which comprises a plurality of photodiodes (PD""s) acting as the photoelectric conversion devices, the PD""s are independent from one another, and the sensitivities of the PD""s are not identical with one another. Therefore, in such cases, such that an image having good image quality may be obtained, it is necessary for the outputs obtained from the respective PD""s to be corrected in accordance with the variation in sensitivity among the PD""s constituting the CCD image sensor.
Also, as illustrated in FIG. 6, in the cases of the CCD image sensor, the relationship between the output signal (i.e., the electric charge amount), which is obtained from each PD acting as the photoelectric conversion device, and the surface illuminance of light incident upon the PD is such that the relationship is approximately linear (i.e., the PD has linearity) until saturation is reached in the electric charge amount. However, the linearity of the PD does not exactly form a straight line. Therefore, in cases where correction values for the correction of the outputs obtained from the respective photoelectric conversion devices (in this example, the PD""s) are to be calculated, such that accurate correction effects may be obtained, it is necessary for the correction value for the correction of the output of each PD to be calculated in accordance with the level of the surface illuminance on the PD.
The primary object of the present invention is to provide a radiation image read-out method, wherein noise due to variation in sensitivity among photoelectric conversion devices constituting a line sensor is capable of being eliminated, and an image having good image quality is capable of being obtained.
Another object of the present invention is to provide an apparatus for carrying out the radiation image read-out method.
The present invention provides a radiation image read-out method, comprising the steps of:
i) linearly irradiating stimulating rays, which have been produced by a line light source, onto an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, with a line sensor comprising a plurality of photoelectric conversion devices, the received light being subjected to photoelectric conversion performed by the line sensor,
iii) moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from a length direction of the linear area of the stimulable phosphor sheet, and
iv) successively reading outputs of the line sensor in accordance with the movement, outputs of the photoelectric conversion devices at respective positions of movement being thereby obtained,
wherein the outputs of the line sensor are corrected in accordance with variation in sensitivity among a plurality of pixel regions of the line sensor, which pixel regions are arrayed along the length direction of the linear area of the stimulable phosphor sheet.
In the radiation image read-out method in accordance with the present invention, as the line light source, a fluorescent lamp, a cold cathode fluorescent lamp, a light emitting diode (LED) array, or the like, may be employed. The line light source may be a light source having a linear shape as in the cases of the fluorescent lamp. Alternatively, the line light source may be a light source operating such that the produced stimulating rays are formed into a line light beam. For example, the line light source may be a broad area laser, or the like. The stimulating rays radiated out from the line light source may be radiated out continuously. Alternatively, the stimulating rays radiated out from the line light source may be radiated out as pulsed stimulating rays, which are radiated out intermittently. From the point of view of reducing noise, the stimulating rays should preferably be pulsed stimulating rays having a high intensity.
As will be understood from the specification, it should be noted that the term xe2x80x9cmoving a stimulable phosphor sheet with respect to a line light source and a line sensorxe2x80x9d as used herein means movement of the stimulable phosphor sheet relative to the line light source and the line sensor, and embraces the cases wherein the stimulable phosphor sheet is moved while the line light source and the line sensor are kept stationary, the cases wherein the line light source and the line sensor are moved while the stimulable phosphor sheet is kept stationary, and the cases wherein both the stimulable phosphor sheet and the line light source and the line sensor are moved. In cases where the line light source and the line sensor are moved, they should be moved together with each other.
The direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor (i.e., the direction different from the length direction of the exposed linear area of the stimulable phosphor sheet) should preferably be the direction approximately normal to the length direction of the exposed linear area of the stimulable phosphor sheet (i.e., should preferably be the minor axis direction). However, the direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor is not limited to the minor axis direction. For example, the stimulable phosphor sheet may be moved with respect to the line light source and the line sensor along an oblique direction with respect to the direction approximately normal to the length direction of the line light source and the line sensor or along a zigzag movement direction, such that approximately the entire surface of the stimulable phosphor sheet maybe uniformly exposed to the stimulating rays.
The line light source and the line sensor maybe located on the same surface side of the stimulable phosphor sheet or on opposite surface sides of the stimulable phosphor sheet. In cases where the line light source and the line sensor are located on opposite surface sides of the stimulable phosphor sheet, the substrate of the stimulable phosphor sheet, or the like, should be formed from a material permeable to the emitted light, such that the emitted light may permeate to the surface side of the stimulable phosphor sheet opposite to the surface on the stimulating ray incidence side.
Also, in the radiation image read-out method in accordance with the present invention, the stimulable phosphor sheet for storing the radiation image may be an ordinary stimulable phosphor sheet comprising a stimulable phosphor for absorbing radiation and storing energy from the radiation, i.e. the radiation image.
Further, the radiation image read-out method in accordance with the present invention may be employed in the radiation image recording and reproducing system proposed in, for example, Japanese Patent Application No. 11(1999)-372978. With the proposed radiation image recording and reproducing system, the radiation absorbing functions and the energy storing functions of the conventional stimulable phosphor are separated from each other, and a phosphor having good radiation absorbing characteristics and a phosphor having good light emission response characteristics are utilized respectively for radiation absorption and radiation image storage. The phosphor having good radiation absorbing characteristics (i.e., a phosphor for radiation absorption) is caused to absorb the radiation and to emit light having wavelengths falling within an ultraviolet to visible region. Also, the phosphor having good light emission response characteristics (i.e., a phosphor for energy storage) is caused to absorb the light, which has been emitted by the phosphor having good radiation absorbing characteristics, and to store energy of the emitted light. The phosphor having good light emission response characteristics, on which the energy of the emitted light has been stored, is then exposed to light having wavelengths falling within a visible to infrared region, which light causes the phosphor having good light emission response characteristics to emit light in accordance with the stored energy. The light having thus been emitted by the phosphor having good light emission response characteristics is successively detected with photoelectric read-out means, and an image signal is thereby obtained. With the proposed radiation image recording and reproducing system, the detection quantum efficiency in the formation of the radiation image, i.e., the radiation absorptivity, the light emission efficiency, the emitted light pickup efficiency, and the like, is capable of being enhanced as a whole. Therefore, in the radiation image read-out method in accordance with the present invention, the stimulable phosphor sheet should preferably contain the phosphor for energy storage described above.
The phosphor for energy storage absorbs the light having wavelengths falling within the ultraviolet to visible region, which light has been emitted by the phosphor for radiation absorption, and stores the energy of the emitted light as the image information. The light having wavelengths falling within the ultraviolet to visible region is the light emitted by the phosphor for radiation absorption when the phosphor for radiation absorption absorbs the radiation. Therefore, the image information having been stored on the phosphor for energy storage is also taken as the radiation image.
The radiation image read-out method in accordance with the present invention is characterized by correcting the outputs of the line sensor in accordance with variation in sensitivity among the plurality of the pixel regions of the line sensor, which pixel regions are arrayed along the length direction of the linear area of the stimulable phosphor sheet. The correction should preferably be performed in the manner described below. Specifically, light having a known light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet may be projected onto the line sensor, and a correction value may be calculated with respect to each of the pixel regions of the line sensor and in accordance with outputs of the pixel regions of the line sensor, which outputs are obtained when the pixel regions of the line sensor receive the projected light. Also, when the radiation image is read out from the stimulable phosphor sheet, the output of each of the pixel regions of the line sensor, which output is obtained when each of the pixel regions of the line sensor receives the light emitted by the stimulable phosphor sheet, may be corrected in accordance with the thus calculated correction value.
The light having the known light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet is the light projected onto the line sensor over the entire area of the light receiving region of the line sensor for the calculation of the correction values. The light having the known light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet is not limited to a linear light beam. However, the light having the known light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet should preferably be a linear light beam.
Ordinarily, the intensity of the stimulating rays, which are linearly irradiated from the line light source onto the stimulable phosphor sheet, is uniform along the length direction of the linear area of the stimulable phosphor sheet. Therefore, the light having the known light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet should preferably be light having uniform light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet.
Also, it may often occurs that the linear stimulating rays, which are irradiated from the line light source onto the stimulable phosphor sheet when the radiation image is to be read out from the stimulable phosphor sheet, has a certain light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet. Therefore, such that more accurate correction effects may be obtained, more accurate correction values should preferably be calculated by linearly projecting light, which has a light intensity distribution corresponding to the light intensity distribution of the stimulating rays along the length direction of the linear area of the stimulable phosphor sheet, onto the line sensor.
Further, as described above, the linearity of each of the photoelectric conversion devices of the line sensor does not exactly form a straight line. Therefore, the radiation image read-out method in accordance with the present invention should more preferably be modified such that correction values, each of which corresponds to one of at least two different levels of incident light intensities upon each of the pixel regions of the line sensor, are calculated, and
the output of each of the pixel regions of the line sensor, which output is obtained when each of the pixel regions of the line sensor receives the light emitted by the stimulable phosphor sheet, is corrected in accordance with a level of an incident light intensity of the emitted light and in accordance with the thus calculated correction values, each of which corresponds to one of the at least two different levels of the incident light intensities.
Furthermore, the projection of the light onto the line sensor and the calculation of the correction values should preferably be performed with one of the techniques described under (1), (2), and (3) below.
(1) The stimulating rays are irradiated onto an area of one surface of a stimulable phosphor sheet, on which a predetermined amount of energy has been stored approximately uniformly (and which has been obtained by irradiating uniform amount of radiation to an entire surface of the stimulable phosphor sheet, i.e. which has been obtained from uniform exposure to the radiation),
the light, which is emitted from the exposed area of the one surface of the stimulable phosphor sheet exposed to the stimulating rays or from an area of the other surface of the stimulable phosphor sheet corresponding to the exposed area of the one surface of the stimulable phosphor sheet when the stimulating rays are irradiated onto the exposed area of the one surface of the stimulable phosphor sheet, is received with the line sensor, and
the correction value with respect to each of the pixel regions of the line sensor is calculated in accordance with the outputs of the pixel regions of the line sensor, which outputs are obtained when the pixel regions of the line sensor receive the light emitted by the stimulable phosphor sheet.
The technique described under (1) has the advantages in that the line light source employed for the radiation image readout from the stimulable phosphor sheet, on which the radiation image has been stored, is capable of being utilized for the projection of the light onto the line sensor for the calculation of the correction value, and in that nonuniformity of the light guiding optical system and nonuniformity of the stimulation optical system are capable of being compensated for.
(2) Stimulating rays are irradiated onto an area of one surface of a uniform, anti-Stokes"" type of phosphor sheet,
light, which is radiated out from the exposed area of the one surface of the anti-Stokes"" type of the phosphor sheet exposed to the stimulating rays or from an area of the other surface of the anti-Stokes"" type of the phosphor sheet corresponding to the exposed area of the one surface of the anti-Stokes"" type of the phosphor sheet when the stimulating rays are irradiated onto the exposed area of the one surface of the anti-Stokes"" type of the phosphor sheet, is received with the line sensor, and
the correction value with respect to each of the pixel regions of the line sensor is calculated in accordance with the outputs of the pixel regions of the line sensor, which outputs are obtained when the pixel regions of the line sensor receive the light radiated out from the anti-Stokes"" type of the phosphor sheet.
The term xe2x80x9canti-Stokes"" type of phosphor sheetxe2x80x9d as used herein means the phosphor sheet, which does not store energy of received light as in the cases of the stimulable phosphor sheet, and which is formed from a phosphor having the properties such that, when the phosphor receives light, the phosphor radiates out light having wavelengths falling within a wavelength region different from the wavelength region of the received light.
The technique described under (2) has the advantages in that an operation for exposing the phosphor sheet to light need not be performed before the stimulating rays are irradiated to the phosphor sheet for the calculation of the correction value.
As a light source for producing the stimulating rays utilized in the technique described under (2), the line light source, which is employed for the radiation image readout from the stimulable phosphor sheet, may be utilized.
(3) Light, which is produced by a reference light source, is projected onto the line sensor, and
the correction value with respect to each of the pixel regions of the line sensor is calculated in accordance with the outputs of the pixel regions of the line sensor, which outputs are obtained when the pixel regions of the line sensor receive the light produced by the reference light source.
The technique described under (3) has the advantages in that the stimulable phosphor sheet obtained from uniform exposure to the radiation or the anti-Stokes"" type of the phosphor sheet need not be prepared for the calculation of the correction value. The reference light source utilized in the technique described under (3) is the light source, which is different from the line light source for the radiation image readout from the stimulable phosphor sheet, and which is provided for the compensation for variation in sensitivity among the pixel regions of the line sensor. The reference light source should preferably be constituted of one of an electroluminescence (EL) device, a light emitting diode (LED) array, and a laser diode (LD) array.
The present invention also provides an apparatus for carrying out the radiation image read-out method in accordance with the present invention. Specifically, the present invention also provides a radiation image read-out apparatus, comprising:
i) a line light source for linearly irradiating stimulating rays on to an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) a line sensor comprising a plurality of photoelectric conversion devices for receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, and performing photoelectric conversion of the received light,
iii) scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from a length direction of the linear area of the stimulable phosphor sheet, and
iv) reading means for successively reading outputs of the line sensor in accordance with the movement in order to obtain outputs of the photoelectric conversion devices at respective positions of movement performed by the scanning means,
wherein the improvement comprises the provision of correction means for correcting the outputs of the line sensor in accordance with variation in sensitivity among a plurality of pixel regions of the line sensor, which pixel regions are arrayed along the length direction of the linear area of the stimulable phosphor sheet.
In the radiation image read-out apparatus in accordance with the present invention, such that the detection quantum efficiency in the formation of the radiation image may be enhanced and an image having good image quality may be obtained, the stimulable phosphor sheet should preferably contain a stimulable phosphor, which is capable of absorbing light having wavelengths falling within an ultraviolet to visible region and thereby storing energy of the light having wavelengths falling within the ultraviolet to visible region, and which is capable of being stimulated by light having wavelengths falling within a visible to infrared region and thereby radiating out the stored energy as emitted light.
The radiation image read-out apparatus in accordance with the present invention is characterized by being provided with the correction means for correcting the outputs of the line sensor in accordance with variation in sensitivity among the plurality of the pixel regions of the line sensor, which pixel regions are arrayed along the length direction of the linear area of the stimulable phosphor sheet. The correction means should preferably comprise light projecting means for projecting light, which has a known light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet, onto the line sensor, and
operation processing means for calculating a correction value with respect to each of the pixel regions of the line sensor and in accordance with outputs of the pixel regions of the line sensor, which outputs are obtained when the pixel regions of the line sensor receive the projected light, and correcting the output of each of the pixel regions of the line sensor, which output is obtained when each of the pixel regions of the line sensor receives the light emitted by the stimulable phosphor sheet, in accordance with the thus calculated correction value.
Ordinarily, the intensity of the stimulating rays, which are linearly irradiated from the line light source onto the stimulable phosphor sheet, is uniform along the length direction of the linear area of the stimulable phosphor sheet. Therefore, in the radiation image read-out apparatus in accordance with the present invention, the light having the known light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet should preferably be light having uniform light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet.
Also, it may often occurs that the linear stimulating rays, which are irradiated from the line light source onto the stimulable phosphor sheet when the radiation image is to be read out from the stimulable phosphor sheet, has a certain light intensity distribution along the length direction of the linear area of the stimulable phosphor sheet. Therefore, in order for more accurate correction effects to be obtained, the radiation image read-out apparatus in accordance with the present invention should more preferably be modified such that the correction means comprises the light projecting means for linearly projecting light, which has a light intensity distribution corresponding to the light intensity distribution of the stimulating rays along the length direction of the linear area of the stimulable phosphor sheet, onto the line sensor, and
the operation processing means for calculating the correction value with respect to each of the pixel regions of the line sensor and in accordance with the outputs of the pixel regions of the line sensor, which outputs are obtained when the pixel regions of the line sensor receive the projected light, and the incident light intensity, and correcting the output of each of the pixel regions of the line sensor, which output is obtained when each of the pixel regions of the line sensor receives the light emitted by the stimulable phosphor sheet, in accordance with the thus calculated correction value.
Further, as described above, the linearity of each of the photoelectric conversion devices of the line sensor does not exactly form a straight line. Therefore, the radiation image read-out apparatus in accordance with the present invention should more preferably be modified such that the correction means calculates correction values, each of which corresponds to one of at least two different levels of incident light intensities upon each of the pixel regions of the line sensor, and
the correction means corrects the output of each of the pixel regions of the line sensor, which output is obtained when each of the pixel regions of the line sensor receives the light emitted by the stimulable phosphor sheet, in accordance with a level of an incident light intensity of the emitted light and in accordance with the thus calculated correction values, each of which corresponds to one of the at least two different levels of the incident light intensities.
Furthermore, the radiation image read-out apparatus in accordance with the present invention should preferably be modified such that the light projecting means irradiates the stimulating rays onto an area of one surface of a stimulable phosphor sheet, on which a predetermined amount of energy has been stored approximately uniformly (and which has been obtained from uniform exposure to the radiation), and
the light projecting means projects the light, which is emitted from the exposed area of the one surface of the stimulable phosphor sheet exposed to the stimulating rays or from an area of the other surface of the stimulable phosphor sheet corresponding to the exposed area of the one surface of the stimulable phosphor sheet when the stimulating rays are irradiated onto the exposed area of the one surface of the stimulable phosphor sheet, onto the line sensor.
In such cases, the line light source employed for the radiation image readout from the stimulable phosphor sheet, on which the radiation image has been stored, is capable of being utilized for the projection of the light onto the line sensor for the calculation of the correction value. Also, in such cases, nonuniformity of the light guiding optical system and nonuniformity of the stimulation optical system are capable of being compensated for.
Also, the radiation image read-out apparatus in accordance with the present invention should preferably be modified such that the light projecting means irradiates stimulating rays onto an area of one surface of a uniform, anti-Stokes"" type of phosphor sheet, and
the light projecting means projects light, which is radiated out from the exposed area of the one surface of the anti-Stokes"" type of the phosphor sheet exposed to the stimulating rays or from an area of the other surface of the anti-Stokes"" type of the phosphor sheet corresponding to the exposed area of the one surface of the anti-Stokes"" type of the phosphor sheet when the stimulating rays are irradiated onto the exposed area of the one surface of the anti-Stokes"" type of the phosphor sheet, onto the line sensor.
In such cases, an operation for exposing the phosphor sheet to light need not be performed before the stimulating rays are irradiated to the phosphor sheet for the calculation of the correction value.
Further, the radiation image read-out apparatus in accordance with the present invention should preferably be modified such that the light projecting means projects light, which is produced by a reference light source, onto the line sensor. In such cases, the stimulable phosphor sheet obtained from uniform exposure to the radiation or the anti-Stokes"" type of the phosphor sheet need not be prepared for the calculation of the correction value.
The reference light source should preferably be constituted of one of an EL device, a LED array, and a LD array.
With the radiation image read-out method and apparatus in accordance with the present invention, the outputs of the pixel regions of the line sensor are corrected in accordance with variation in sensitivity among the plurality of the pixel regions of the line sensor. Therefore, noise due to variation in sensitivity among the photoelectric conversion devices constituting the pixel regions of the line sensor is capable of being eliminated, and an image having good image quality is capable of being obtained.
With the radiation image read-out method and apparatus in accordance with the present invention, wherein the stimulable phosphor sheet contains the phosphor for energy storage described above, the image quality of the obtained image is capable of being enhanced even further.
With the radiation image read-out method and apparatus in accordance with the present invention, the correction values, each of which corresponds to one of at least two different levels of incident light intensities upon each of the pixel regions of the line sensor, may be calculated. Also, the output of each of the pixel regions of the line sensor, which output is obtained when each of the pixel regions of the line sensor receives the light emitted by the stimulable phosphor sheet, may be corrected in accordance with the level of the incident light intensity of the emitted light and in accordance with the thus calculated correction values, each of which corresponds to one of the at least two different levels of the incident light intensities. In such cases, a more accurate correction is capable of being performed.